Modern integrated circuits, Class D, allow the creation of small energy-saving audio amplifiers, which can be mounted, For example, inside the column. This makes it possible to create active speakers, the most popular of which are the ones, which have in its design subwoofers. The article describes the construction of a subwoofer based on integrated circuit TPA3136.
The apparatus consists of two functional blocks: lowpass filter with adjustable cutoff frequency based on the popular TLC274 operational amplifier and power amplifier, operating in a bridge configuration,, the chip TPA3136AD2. Driving the power amplifier, It comprises two channel bridge power class D amplifier with common switching circuits, mute and protection.
In the circuit, two power amplifier configured for parallel operation PBTL, that allows you to get around 20 W into 4 Ohms and the supply voltage 14,4 AT.
Due to the high efficiency of the chip, from reaching the load 4 ohms to 90%, It can be operated without a heatsink, with heat removal through the copper on both sides of the printed circuit board.
Scheme lowpass filter is shown in Figure 1.
The stereo signal from the input terminal IN is connected to the adder (U2-1) with increased, adjustable potentiometer SGain. After adding and adjusting the signal level fed to the low pass filter (U2-4) with a cutoff frequency, adjustable potentiometer SFQ. The signal from the filter output is fed into buffers (U2-2, U2-3). One of them works phase inversion signal in the configuration (U2-3). signals the inverter has two functions: it generates a balanced signal through the switch and allows the phase signal PH change, power amplifier control. Schematic diagram of the power amplifier shown in Figure 2.
The filtered signal is symmetric (SUBN / P) connected to the chip U1 (TPA3136AD2) through capacitors C1, C2, separating a DC component, where it is amplified. capacitors C9, C10 are elements of a bridge circuit polarizing. The remaining capacitors filtered power U1. Output filter FB12, C11, C12 removes noise input from the modulation process and. PW LED displays, that power is on. The power supply in the range 9 … 14,4 The connector connects to the PWR. The supply voltage is filtered through diode D1, R13 resistor, Capacitors C15 and CE3.
Authors sample assembled on a double-sided printed circuit board shown in Figure 3. Installation of components is typical and does not require a description. In case TPA3136AD2 heat is removed through the bottom radiator insert, which must be properly soldered to the ground. To improve heat dissipation to the U1 can be attached to a small aluminum heatsink.
Assembled from the functional components of the amplifier is immediately after power. Examples subwoofer filter characteristics shown in Figure 4.
The system is designed to work with line level. When it comes to work directly with the output of the power amplifier, you need to select the input voltage dividers. If the cutoff frequency must be above 250 Hz, instead SFQ potentiometer 2 × 25 KW can solder 2 × 50 k.